Origin of skillful stone-tool-sharpening method pushed back more than 50,000 years

October 28, 2010

Pictured is a Still Bay bifacial point from Blombos Cave in South Africa made of silcrete and finished by pressure flaking, primarily at the tip. Credit: Image courtesy Science/AAAS

A highly skillful and delicate method of sharpening and retouching stone artifacts by prehistoric people appears to have been developed at least 75,000 years ago, more than 50,000 years earlier than previously thought, according to a new study led by the University of Colorado at Boulder.

The new findings show that the technique, known as pressure flaking, took place at Blombos Cave in South Africa during the Middle Stone Age by anatomically modern humans and involved the heating of silcrete -- quartz grains cemented by silica -- used to make tools. Pressure flaking takes place when implements previously shaped by hard stone hammer strikes followed by softer strikes with wood or bone hammers are carefully trimmed on the edges by directly pressing the point of a tool made of bone on the stone artifact.

The technique provides a better means of controlling the sharpness, thickness and overall shape of bifacial tools like spearheads and stone knives, said Paola Villa, a curator at the University of Colorado Museum of Natural History and a study co-author. Prior to the Blombos Cave discovery, the earliest evidence of pressure flaking was from the Upper Paleolithic Solutrean culture in France and Spain roughly 20,000 years ago.

"This finding is important because it shows that modern humans in South Africa had a sophisticated repertoire of tool-making techniques at a very early time," said Villa. "This innovation is a clear example of a tendency to develop new functional ideas and techniques widely viewed as symptomatic of advanced, or modern, behavior."

A paper on the subject was published in the Oct. 29 issue of Science. Other study co-authors included Vincent Mourre of the French National Institute for Preventive Archaeological Research in France and Christopher Henshilwood of the University of Bergen in Norway and director of the Blombos Cave excavation. The research was funded by the Wenner Gren Foundation of New York.

"Using the pressure flaking technique required strong hands and allowed toolmakers to exert a high degree of control on the final shape and thinness that cannot be achieved by percussion," Villa said. "This control helped to produce narrower and sharper tool tips." The bifacial points, known as Still Bay points, likely were spearheads, she said.

The authors speculated that the pressure flaking technique may have been invented in Africa and used sporadically before its later, widespread adoption in Europe, Australia and North America. North American archaeologists have shown that Paleoindians used the pressure flaking technique to fashion stone points likely used to hunt a menagerie of now-extinct mammals like mammoths, mastodons and ancient horses.

With the exception of obsidian, jasper and some high-quality flint, few stone materials can be pressure flaked without first heating them, Villa said. While there is evidence of silcrete heating some 164,000 years ago at the Pinnacle Point site in South Africa, the Blombos Cave artifacts are the first clear evidence of the skillful pressure flaking technique being used to carefully shape, refine and retouch tools, said Villa.

There are several ways to confirm whether silcrete has been heat-treated, Villa said. Archaeologists at Pinnacle Point used two common methods called thermoluminescence and archaeomagnetism that require the destruction of stone tool samples, as well as a non-destructive technique known as maximum gloss analysis.

Villa, Mourre and Henshilwood used a visual method for the Blombos Cave artifact analysis based on the contrast between heated and unheated tool surfaces observed microscopically at low magnification. While the removal of flakes from unheated silcrete produces scar surfaces with a rough, dull texture, heat-treated silcrete scar surfaces have a smooth, glossy appearance, said Villa.

The researchers analyzed 159 silcrete points and fragments, 179 other retouched pieces and more than 700 flakes from a layer in Blombos Cave linked to the so-called Still Bay industry, a Middle Stone Age tool manufacturing style that started roughly 76,000 years ago and which may have lasted until 72,000 years ago. The researchers concluded that at least half of the ancient, finished points at Blombos Cave were retouched by pressure flaking.

In addition to the microscopic analysis of the tools, the team also used experimental replication to show that pressure flaking was used in the final retouching phase of the points. The shaping of both heated and non-heated tools -- known as knapping -- was done by Mourre using silcrete chunks collected by Henshilwood from outcrops roughly 20 miles from Blombos Cave.

The silcrete samples used in the replication stage of the study were heated by Henshilwood in collaboration with Kyle Brown of Arizona State University, who published a 2009 paper in Science on the heat-treatment of silcrete in South Africa.

The team members compared attributes of points and flakes created for the experiments by percussion and pressure with points and flakes found in Blombos Cave, finding that unheated silcrete chunks first shaped with quartzite stone hammers and further worked on with wooden hammers known as billets could not be pressure flaked.

"Pressure flaking adds to the repertoire of technological advances during the Still Bay (period) and helps define it as a time when novel ideas were rapidly introduced," wrote the authors in Science. "This flexible approach to technology may have conferred an advantage to the groups of Homo sapiens who migrated out of Africa about 60,000 years ago."

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Mythbusters tested whether a stone arrow head actually improved performance as compared to a sharp wooden stick, and found that the difference was hardly even noticeable.[...]They concluded that stone tips were probably more for ornamental purposes than practical purposes.

Yes, and "Mythbusters" are honored the world over for their scientific accuracy and adherence to rigid testing protocol.

Exhaustive analysis aside, what the mythbusters failed to note in their conclusions is that this toolmaking technology PUPOSEFULLY includes, as part of it's design, either a) the GEOMETRY to create a "wound gap" or b) a "blood groove", specifically to cause a muchly increased rapid bleed out in prey animals.

When you are dependent upon your own two legs to run down the only animal that you've been able to shoot all day, in order to feed your family, with temp dropping, darkening skies, snow starting, and roar of a cave lion nearby, a chase of only 100 yards vs a mile is a lifesaver, and this intentional "accelerated bleed" design feature represents a quantum leap in lithic technology. PRECISELY because it speeds up the killing process of prey/enemies.

The conclusion by the "mythbusters" that the additional time required to manufacture these points "wasn't worth it"(unless, of course, you consider preservation of your life, and those you care about "worth it") only goes to show how valid their "science-ism" is and how opportunistically self-serving your definition of (acceptable evidentiary level) Science is.

Given the short, brutal nature of their lives, the simple fact that they spent the enormous amount of time to make stone points is proof enough that it was worth the effort. As for the statement "[t]he only difference was that the arrowhead made a slightly wider entrance wound," this implies that the arrows (or stake)) were pulled out of the target to facilitate the comparison of entrance sizes. However, the main difference would be when the projectile is still in the target. A projectile which flares smoothly from a sharpened point to a cylinder of constant radius will completely fill the wound and block blood flow (which is why medical experts agree that if you are injured by such an object, the best thing to do is leave it in to avoid bleeding out). The shaft of an arrow would not be wide enough to fill the hole left by a wider stone tip, hence bleeding.

@Quantum - Efficacy hunting game vs fighting another human are very different topics... You can have your sharpened stick team and I take my scary stone spear tip team - lets see how it goes... btw - my scary stone tip team can also use our weapons in many directions to cut your stick team - while the stick only team makes only bruises while slashing... oh I forgot - humans didn't fight each other till modern times

I expect a sharpened stone spear tip would cut and penetrate thick, tough hides much easier than a sharp stick; especially if trying to stick the dang thing in while running flat out over rough terrain. Hope the investigators didn't stumble and bust their "myths" while trying to run down that mastodon. Try cutting shoe leather with a sharp stick, then try a sharpened stone tip. Meanwhile, I'll trust the guys who did this for a living for thousands of years.

I expect a sharpened stone spear tip would cut and penetrate thick, tough hides much easier than a sharp stick; especially if trying to stick the dang thing in while running flat out over rough terrain. Hope the investigators didn't stumble and bust their "myths" while trying to run down that mastodon. Try cutting shoe leather with a sharp stick, then try a sharpened stone tip. Meanwhile, I'll trust the guys who did this for a living for thousands of years.

You expect wrong.

They tested ballistics gel with a hide covering, and there was no appreaciable difference in penetration. In fact, the hide made no difference at all.

I expect a sharpened stone spear tip would cut and penetrate thick, tough hides much easier than a sharp stick; especially if trying to stick the dang thing in while running flat out over rough terrain. Hope the investigators didn't stumble and bust their "myths" while trying to run down that mastodon. Try cutting shoe leather with a sharp stick, then try a sharpened stone tip. Meanwhile, I'll trust the guys who did this for a living for thousands of years.

Have you ever actually killed an animal?

My brother and cousins and I used to hunt with 10 minute special, home-made bows and arrows back when I was like 8 or 9 years old.

Funny thing. Out of curiosity, I just went to Myth Busters web site that showed their results from every show from every season. Couldn't find a thing about spears or stone spear points. Is that what you call busted?http://mythbustersresults.com/

I have both lived on a farm and used sharp stone tools - not out of necessity. I found it quite quick to put an edge on a stone tool and they could be much sharper than your average knife.

Coupled with that I too am a martial artist and also - not recently an archer. When shooting targets you use a pointed stick yes it has a steel end but basically it is a stick with a point on it. For shooting game your change to a wide blade tip. Much more efficient and useful. In fact a target arrow if left in a wound will not cause much blood loss and an animal could easily survive for a time what would otherwise be a fatal wound.

I have a friend that is a vet and they have treated cats and dogs that were shot with target arrows this is fact. Whereas a much larger animal like a boar does not survive long after being shot with a wide blade arrow.

First, Quantum is correct (and it's even a PhysOrg article): http://www.physor...390.html that they did *projectile* tests. So, what were those Native Americans up to anyway working (hundreds of thousands of) rock arrow points - ceremonial? If the dating is correct, it proves that somebody said, "I can't cut meat with a stick, but rock works great!" ... Side-note, I go to PhysOrg to look at the comments... there really are some creative thinkers out there and it isn't necessary to slam others views (outright) but to educate all of us.

When you are dependent upon your own two legs to run down the only animal that you've been able to shoot all day, in order to feed your family, with temp dropping, darkening skies, snow starting, and roar of a cave lion nearby, a chase of only 100 yards vs a mile is a lifesaver, and this intentional "accelerated bleed" design feature represents a quantum leap in lithic technology. PRECISELY because it speeds up the killing process of prey/enemies.

What about the durability of a stone arrowhead? A stone arrowhead would be able to be used many more times than wooden arrowheads which could bean less arrows needed to be made for each hunting trip. Also, stone arrowheads would generally stay sharp whereas wooden arrowheads would dull quickly with use (assuming you could get repeated use out of them at all).

Think about hardness... If you shoot a wooden arrow into a tree, since the hardness of the wood in the arrow and the tree should be relatively similar, the head of the wooden arrow is likely to deform and/or dull. A stone arrowhead would sink into the tree, but could likely be removed and reused and still be nearly as sharp.

This article certainly poses a great question! Why did everyone use stone tips?

Sharpened sticks would have an advantage in that if the tip is damaged, it's quickly and easily repaired. And, it'd be easy enough to carve or attach barbs for a similar bleed out effect.

I wonder how fire-hardened sticks might compare? I know from personal experience that fire-hardened spear points are pretty tough (less prone to splintering).

Another consideration: Sticks alone (coming from many possible species of trees) might have widely variable properties that would make stone tips more attractive for their reliability. That is, they could "standardize" the manufacture of arrows, without significant regard to the material qualities of the shaft.

Anyway, my great uncle had a huge collection of arrowheads. The craftsmanship was incredible. And you can't deny that they held an edge. You could mount ancient arrowheads on new shafts and use them just as effectively today!

Hi, one thing seemingly has not yet been mentioned. Due to the increased weight at the top, the arrow should have a trajectory easier to be controlled. At least it has been lke this in my youth for our self made arrows.

Hi, one thing seemingly has not yet been mentioned. Due to the increased weight at the top, the arrow should have a trajectory easier to be controlled. At least it has been lke this in my youth for our self made arrows.

I would agree with this. As a child when we made 'bows and arrows' accuracy and extra range would be achieved by wrapping a length of steel wire around the tip of the arrow. The amount of wire would have to be gauged relative to the weight and length of the arrow for best results. If the stone arrowhead weight is taken into account the dimensions of the original arrow could possibly be calculated assuming our ancestors were interested in the most efficient tool possible.

Another consideration is mass/momentum to size ratio. By using stone tips, the arrow is thereby given greater mass for its size, thus enabling smaller (less cumbersome) arrows to have the same striking force as larger, sharpened sticks.

I also agree with Ramadamses and Liamo above. I think, with a weighted tip, they'd tend to be less vulnerable to aerodynamic imperfections and crosswinds and such.

Of course, it's also possible they did use sharpened sticks too. There's just no way to tell, as organic materials aren't preserved.